In recent years, integrated circuits using an SOI (silicon on insulator) substrate that includes a thin single crystal semiconductor layer formed on an insulating surface have been developed instead of those using a bulk silicon wafer. The characteristics of the thin single crystal silicon film formed on the insulating surface make it possible to completely separate transistors formed in the integrated circuit. In addition, fully-depleted transistors can be obtained, thereby realizing a semiconductor integrated circuit with high added value such as high integration, high-speed driving, and low power consumption.
One of the known methods for manufacturing an SOI substrate is Smart Cut (registered trademark). The use of Smart Cut allows an SOI substrate having a single crystal silicon film to be manufactured not only on a silicon substrate but also on an insulating substrate such as a glass substrate (for example, see Patent Document 1). An SOI substrate having a single crystal silicon thin film formed on a glass substrate is generally manufactured by Smart cut as follows. First, a silicon dioxide film is formed on a surface of a single crystal silicon wafer. Next, hydrogen ions are implanted into the single crystal silicon wafer to form a hydrogen ion-implanted layer at a predetermined depth in the single crystal silicon wafer. Then, the single crystal silicon wafer into which the hydrogen ions have been implanted is bonded to a glass substrate with the silicon dioxide film interposed therebetween. After that, a heat treatment is performed, whereby a thin film of the single crystal silicon wafer into which the hydrogen ions have been implanted is separated with the hydrogen ion-implanted layer serving as a cleavage plane. Thus, a single crystal silicon thin film can be formed on the bonded glass substrate. Smart Cut is also referred to as a hydrogen ion implantation separation method.